Traditional chalkboards and whiteboards have significant drawbacks. First, they do not readily allow a user's writing to be superimposed over information electronically displayed on an electronic display. Second, they require a specialized writing surface that is compatible with chalk, dry erase markers, or similar writing tools. Third, the written information is not easily captured electronically for computerized processing or display. While some whiteboards have electronic scanning capability, these systems are typically costly for large whiteboards as a scanning mechanism must typically span an entire dimension of the whiteboard and be configured for mechanical movement across the other dimension of the whiteboard.
Written information is often electronically captured using an electronic touchpad that translates the motion of a stylus, a user's finger, or another pointing device into electronic information. The information is typically captured relative to a position of the stylus, pointer, or finger on a surface or on a display screen. Touchpads are commonly overlaid on a display screen, such as on a smartphone or tablet computer. Touchpads are also sometimes implemented in or on a non-display surface such as a digitizing tablet. A touchpad typically allows information to be electronically captured more efficiently than other methods as the user is not required to enter the information using a traditional input device such as a keyboard or mouse. In addition, the touchpad enables the user to provide freehand or freeform written input.
Touchpads typically operate using one of several methods including capacitive sensing, conductance sensing, and/or using a pressure sensitive membrane. Each of these methods requires that the surface be overlaid with electrical circuitry and/or the mechanical means which enable the surface to be touch sensitive. The cost of adding touch sensitive capability to larger displays increases proportionally with the area of the screen. Consequently, touch input capabilities can be prohibitively expensive as display sizes increase. For this and other reasons, large numbers of displays are sold without touch input capability. It is desirable to add touch input capabilities to these displays in a cost effective manner. In addition, it may be desirable for a user to provide written input using a stylus or finger on a surface other than on a display.